An electrophotographic apparatus employing an electrophotographic method primarily includes an electrophotographic photosensitive member (hereinafter, also simply referred to as “photosensitive member”), a charging member, an exposing device, a developing device, a transfer device and a fixing device. As the charging device, a contact charging member which charges the surface of a photosensitive member by applying a voltage (a voltage of a DC voltage only or a voltage of the DC voltage superimposed with an AC voltage) to the charging member brought into contact with or closely disposed on the surface of the photosensitive member is commonly employed.
In order to stabilize the charging of a photosensitive member induced by contact charging, Patent Literature 1 (PTL 1) discloses a charging member for contact charging including a surface layer having a protrusion derived from a resin particle or the like on the surface. By using such a charging member, the charging of the photosensitive member is stabilized. However, when the charging member described in Patent Literature 1 comes into contact with the photosensitive member, the contact pressure concentrates on the protrusion derived from the resin particle on the surface of the charging member (charging roller), and as a result, non-uniform abrasion occurs on the surface of the photosensitive member in a long-term use, which may cause a vertically streaked image defect due to the non-uniform abrasion.
To address this problem, Patent Literature 2 (PTL 2) proposes a charging member including an electro-conductive resin layer containing a bowl-shaped resin particle having an opening, wherein the charging member has an uneven shape derived from the opening and edge of the bowl-shaped resin particle on the surface of the charging member. By using the charging member described in Patent Literature 2, the contact pressure on a photosensitive member is relaxed by deforming the edge of the opening of the bowl-shaped resin particle (hereinafter, also simply referred to as “edge”) on the surface of the charging member. For the above reason, the non-uniform abrasion of the photosensitive member can be suppressed even in a long-term use.